Handover during secondary cell group failure

Abstract

A user device operating in dual-mode connectivity with a master node and a secondary node detects a failure of a secondary cell group associated with the secondary node (1104). In response, the user device suspends an secondary cell group transmission (1106). The user device generates a message related to a status of the SCG for transmission to the MN (1108) and transmitting the message to the MN when the SCG transmission is suspended (1110).

What is claimed is: 
     
       1. A method in a base station operating as a master node (MN) for performing a handover procedure, the method comprising:
 configuring a user equipment (UE) that operates in dual connectivity (DC) with the MN and a secondary node (SN) with one or more data radio bearers (DRBs) associated with a secondary cell group (SCG) of the SN; 
 in the event that all of the one or more DRBs are determined to be suspended due at least in part to a failure of the SCG, determining that a handover procedure should be performed for the UE; and 
 initiating the handover procedure. 
 
     
     
       2. The method of  claim 1 , further comprising: receiving an indication of failure of the SCG from the UE. 
     
     
       3. The method of  claim 2 , further comprising: 
       in a first instance:
 receiving the indication of failure of the SCG in a dedicated message for reporting SCG failure, associated with a protocol for controlling radio resources, and 
 determining that the handover procedure is allowed; and 
 
       in a second instance:
 receiving the indication of failure of the SCG in a message for reconfiguring a radio connection, associated with the protocol for controlling radio resources, and 
 determining that the handover procedure is not allowed. 
 
     
     
       4. The method of  claim 3 , further comprising, in the second instance, subsequently to determining that the handover procedure is not allowed:
 transmitting to the UE a command to resume the suspended DRB; and 
 
       in response to receiving an indication that the UE has resumed the suspended DRB, determining that the handover procedure is not allowed. 
     
     
       5. The method of  claim 1 , further comprising:
 receiving signal measurement data for (i) a downlink carrier frequency on which the UE currently operates and (ii) a downlink carrier frequency to which the UE can be handed over; 
 wherein determining that the handover procedure should be performed is based on the signal measurement data. 
 
     
     
       6. The method of  claim 1 , wherein the base station is a first base station, and wherein initiating the handover procedure includes:
 transmitting a handover request to a second base station, 
 receiving, from the second base station, an acknowledgement of the handover request; and 
 transmitting to the UE a command to hand over to the second base station. 
 
     
     
       7. The method of  claim 1 , wherein the base station is a first base station, and wherein initiating the handover procedure includes:
 transmitting to a core network (CN) an indication that a handover to a second base station is required. 
 
     
     
       8. The method of  claim 1 , wherein initiating the handover procedure includes:
 handing over the UE from a cell of the base station to a second cell of the base station. 
 
     
     
       9. The method of  claim 1 , wherein initiating the handover procedure includes handing over the UE from a first distributed unit (DU) of the base station to a second DU of the base station. 
     
     
       10. The method of  claim 9 , wherein handing over the UE includes:
 transmitting to the UE a reconfiguration command associated with a protocol for controlling radio resources, the reconfiguration command including a cell group configuration. 
 
     
     
       11. A base station including processing hardware and configured to:
 configure a user equipment (UE) that operates in dual connectivity (DC) with a master node (MN) and a secondary node (SN) with one or more data radio bearers (DRBs) associated with a secondary cell group (SCG) of the SN; 
 in the event that all of the one or more DRBs are determined to be suspended due at least in part to a failure of the SCG, determine that a handover procedure should be performed for the UE; and 
 initiate the handover procedure. 
 
     
     
       12. A method in a user equipment (UE) operating in dual connectivity (DC) with a master node (MN) and a secondary node (SN) for performing a handover procedure, the method comprising:
 obtaining one or more data radio bearers (DRBs) associated with a secondary cell group (SCG) of the SN; 
 determining a failure of the SCG; 
 in response to the failure, suspending all of the one or more DRBs; 
 transmitting an indication of the failure to the MN; and 
 performing a handover procedure when all of the one or more DRBs are suspended. 
 
     
     
       13. The method of  claim 12 , wherein transmitting the indication of the failure to the MN includes transmitting a dedicated message for reporting SCG failure, associated with a protocol for controlling radio resources. 
     
     
       14. The method of  claim 12 , further comprising:
 generating signal measurement data in (i) a cell in which the UE currently operates and (ii) a cell to which the UE can hand over; and 
 transmitting the signal measurement data to the MN. 
 
     
     
       15. The base station of  claim 11 , wherein to determine that the DRB has been suspended, the base station is configured to receive an indication of failure of the SCG from the UE. 
     
     
       16. The base station of  claim 15 , further configured to:
 in a first instance: (i) receive the indication of failure of the SCG in a dedicated message for reporting SCG failure, associated with a protocol for controlling radio resources, and (ii) determine that the handover procedure is allowed; and 
 in a second instance: (i) receive the indication of failure of the SCG in a message for reconfiguring a radio connection, associated with the protocol for controlling radio resources, and (ii) determine that the handover procedure is not allowed. 
 
     
     
       17. The base station of  claim 16 , further configured to:
 in the second instance, subsequently to determining that the handover procedure is not allowed: 
 transmit to the UE a command to resume the suspended DRB; and 
 in response to receiving an indication that the UE has resumed the suspended DRB, determine that the handover procedure is not allowed. 
 
     
     
       18. The base station of  claim 11 , further configured to:
 determine whether all of one or more DRBs with which the UE is configured are suspended; and 
 when not all of the one or more DRBs are suspended, determine that the handover procedure is allowed. 
 
     
     
       19. The base station of  claim 11 , further configured to:
 receive signal measurement data for (i) a downlink carrier frequency on which the UE currently operates and (ii) a downlink carrier frequency to which the UE can be handed over; 
 wherein determining that the handover procedure should be performed is based on the signal measurement data.